Earths rotation

Last Edited By Krjb Donovan
Last Updated: Mar 11, 2014 07:55 PM GMT


i havnt noticed before, but i was watching the moon at about 130 in the morning in the united states (washington state) and it was moving relativly fast, i lined it up with my roof and it traveled its own diameter in about 12 seconds, i thought that was supposed to take 3 min, so i line a few stars up and they also moved noticably in a few seconds. is this normal or (this is a stupid question) is the earth rotating faster?


Hi, Jeff, No no..the earth is still faithfully doing that which it has done for 4.5 billion years! It hasnt speeded up a bit. On the contrary, thanks to the conservation of angular momentum, and tidal locking, the moon recedes away from the earth at 3.8 cm/year and slows down the earth as a consequence.

The moon travels roughly 360 degrees / 28 days = 12.857 deg/day or 12.857 / 24 hours = 0.53571 degrees / hour or 0.53571 / 60 = 0.008928 degrees / min.

The moon subtends about 0.52 degrees angle when viewed from the earth's surface.

That means, to traverse its own width at 0.008928 degrees / min, it will take (0.52/0.008928) min time. That equals 58.243 or roughly an hour. [for independent confirmation refer:- see para 2].

Obviously if the moon traversed its diameter in 12 seconds, 1 - Atmospheric distortion caused that fast movement,

   (happens near the horizon, due to refraction) 

2 - Your point of reference moved with reference to you

I believe the 2nd must have happened.

But is it possible that you were using high power binocs etc?

At higher power, the image scrolls out of view pretty fast.

Check out again in this light. regards Jayen


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